This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of the type which utilizes non-coil springs. Box spring assemblies of this general type have been known since 1964, the first such spring assembly being disclosed in U.S. Pat. No. 3,286,281. Subsequently issued patents disclosing the same general type of box spring assembly are: U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 4,060,862; 4,120,058; 4,131,961; 4,195,376; 4,218,790; 4,238,861; 4,251,892; 4,253,208; 4,339,834; 4,470,584; 4,739,977 and 4,779,293.
Box spring assemblies of the general type shown in the above list of patents, all of which are owned by the assignee of this application, are advantageous with respect to the conventional box spring assemblies using coil springs because they provide a desired stiffer foundation for the mattress and contain a reduced amount of wire. These box spring assemblies are also advantageous from the standpoint of prolonged service life, ease of assembly, and cost of manufacture.
Additional box spring assemblies of this general type are shown in U.S. Pat. Nos. 3,546,723; 3,596,299; 3,722,013; 3,825,960; 3,833,948; 3,835,485; 3,869,740; 3,990,121; and 4,000,531.
The principal object of this invention is to provide a spring for a box spring assembly which has improved limited deflection characteristics to avoid overstressing of the spring during loading in combination with an upright column support which maximizes lateral stability at full deflection. The lateral stability of the limited deflection spring helps to insure that the spring will move in a substantially straight downward direction during deflection, thereby minimizing skewness that can result in permanent deformation of the spring from unbalanced shock loading. In addition, the upright columns in the spring are configured so that they diverge and the angles of divergence can be varied between individual spring elements to optimize the lateral stability and floatation properties of the platform surface of the box spring assembly while providing very strong resistance to relatively straight down impact loading.
Each of the springs according to the present invention has a unitary wire body having a foot portion, an upright yieldable portion extending upward from the foot portion and a load bearing portion at the upper end of the upright portion. The load bearing portion is a generally horizontal deck attaching portion of the wire body which is clipped, interlocked or otherwise attached to a generally horizontal wire mattress support deck which is in turn spaced vertically above a generally horizontal frame. The foot portion of the limited deflection spring according to the present invention is attached to the generally horizontal frame.
The upright portion of the limited deflection spring includes a pair of horizontally spaced upright columns which diverge relative to each other and are suspended between the foot portion and the loading bearing portion by separate vertically yieldable portions. Each vertically yieldable portion is a torsion bar system which includes a pair of generally horizontal upper and lower torsion bars connected together by a common central connecting bar.
In one embodiment of the limited deflection spring according to the present invention, the divergent upright columns diverge upwardly so as to position the lower ends of the upright columns relatively close together beneath the load bearing portion. This arrangement moves the upright columns toward a generally vertical orientation at full deflection thus allowing the deck attaching portion or load bearing portion to be able to tilt, thus giving a floatation property to the mattress support deck.
Another embodiment of the present invention includes downwardly diverging upright columns which, at full deflection, provide a wide base trapezoidal support to the load bearing portion. In this arrangement, the angle between the upright columns increases as the spring is moved from the unloaded to the fully deflected position. This system forms a trapezoid having a wider stance at the base at full deflection which maximizes lateral stability. The lateral stability increases as the spring is actuated. This arrangement also helps to guide the spring in a more straight vertical deflection, thus minimizing skewness that can result in permanent deformation of the spring from unbalanced shock loading.
In contrast, in the first embodiment above described, having upwardly divergent upright columns, the angle between the upright columns tends to decrease as the spring is compressed between the unloaded and the fully deflected positions and forms a narrow base at full deflection. This allows the load bearing portion to tilt under asymmetric loading enhancing the floatation property.
In both embodiments of the present invention, the upright columns are suspended between the mattress support deck and the frame by separate torsion bar systems connecting the upright columns to the load bearing portion and to the foot portion, respectively. This arrangement provides an improved impact resistance.
The spring elements may also be mixed within an individual box spring assembly arrangement depending upon the relative importance of lateral stability or floatation properties which are desired with some mattress designs. For example, springs of the first embodiment with upwardly divergent columns may be positioned in the interior of the mattress support deck to enhance the floatation characteristics while springs of the second embodiment with downwardly divergent columns are arranged around the perimeter to provide improved shock loading and lateral stability along the sides of the mattress support deck. Thus, a combination of the spring elements may be utilized to achieve an overall response that is particularly desirable in a foundation support system.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the following description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings: